The primary goal has been the elucidation of the structures of reactive metabolites which are responsible for the carcinogenic, cytotoxic, and mutagenic activity of benzo[a]pyrene and other polycyclic aromatic hydrocarbons. The approach taken consists of: i) synthesis of primary oxidative metabolites as well as selected secondary oxidative metabolites, ii) study of the metabolism of these hydrocarbons with liver microsomes, as well as with purified and reconstituted cytochrome P-450 systems with and without epoxide hydrolase, iii) tests for inherent mutagenicity of the synthetic metabolites toward bacterial and mammalian cells, iv) elucidation of the roles of the cytochrome P-450 system and epoxide hydrolase in potentiating or obliterating the mutagenicity of these metabolites, v) determination of the carcinogenic activity of these compounds, vi) determination of the rate of formation and nature of the products formed when reactive metabolites such as arene oxides and diol epoxides react with biopolymers and less complex model compounds, and vii) search for compounds capable of preventing the tumorigenic action of bay-region diol epoxides. A general theory of hydrocarbon-induced carcinogenesis, the bay-region theory, has been formulated and its predictions are being tested with synthetic potential metabolites of several hydrocarbons. Current studies have shown that a bay-region 3,4-diol-1,2-epoxide of benz[c]acridine is an ultimate carcinogen. Optically active dihydrodiols and diol epoxides have been prepared to test the theory with dibenz[c,h]acridine derivatives. Despite the low tumorigenicity of 6-fluorobenzo[a]pyrene on mouse skin, the hydrocarbon is metabolized to bay-region diol epoxides as efficiently as is benzo[a]pyrene. Our model for the catalytic binding site for cytochrome P-450c has been probed by studying the formation of optically active naphthalene and anthracene 1,2-oxides. 1,2,3,4-Tetrahydrobenz[a]-anthracene (3R,4S)-epoxide has been identified as the best presently known substrate for microsomal epoxide hydrolase and is about 8-fold more active than phenanthrene 9,10-oxide. A novel pyrrole carboxamidine which causes convulsions in mice has been isolated from the tropical plant Brunfelsia grandiflora.